The Universal Serial Bus (“USB”) was designed to provide a serial communication channel between computers and peripheral devices. For example, USB can connect computer peripherals such as such as mice, keyboards, gamepads, joysticks, scanners, external drives, etc. to a computer. While USB was designed for personal computers it has become commonplace on battery powered computerized devices such as PDAs, music players and cellular telephones which use USB for both data communication and to recharge their batteries. The design of USB is standardized by the USB Implementers Forum (USBIF), an industry standards body incorporating leading companies from the computer and electronics industries.
There are several types of USB connectors approved by the USBIF, including those with four contacts (pins or sockets), such as the USB-A and the USB-B connectors, as well as those with five contacts (pins or sockets), such as the mini/micro-A, mini-micro-B and mini/micro AB. Most computers, including laptop computers, have several USB-A connectors, each of which has a power (VBUS) contact, ground (GND) contact and two data line contacts (D+ and D−).
Laptop computers are becoming increasingly popular. In order to preserve battery life, most laptop computers have “inactive” modes where they are not fully on or fully off, such as “sleep”, “standby” and certain “hibernate” modes. During operation, such computers are considered to be in their “active” state, and their batteries may last for a number of hours. However, by limiting current draws, the batteries of computers in an “inactive” state can last for days. While the terminology can vary from manufacturer to manufacturer, a standard operating mode for a laptop computer is often referred to as an “S0” state, a “standby” mode is often referred to as an “S3” state, a “hibernate” mode is referred to as an “S4” state, and a “shut-down” mode is referred to as an “S5” state. The S1 and S2 states are throttle-back modes and are usually not apparent to users of a laptop computer.
With some exceptions, laptop computers can charge compliant USB devices that are plugged into a USB connector port of the computer when the computers are in an active or S0 state. In such cases, the laptop computer is considered to be a “USB host.” The devices that can be charged through the USB include, but are not limited to, cellular telephones, music players, PDAs etc., collectively referred to herein as “USB devices.” The ability to charge USB devices through the same USB connector port used for the transfer of data is very convenient and is becoming increasingly popular.
It should be noted that USB devices that do not conform to accepted standards (“non-compliant USB devices”) can always draw current from a USB connector that has power on its VBus contact. However, there is strong and increasing desire for USB devices to be compliant with USB standards. For example, USBIF rules specify that a USB device (one type of “compliant USB device”) can only draw current from a computer when the computer is in an active mode and gives its permission. For example, some laptops will not allow charging through a USB connector if it is running solely on battery power. This means that if a laptop computer is in an inactive mode the USB device cannot be charged through the laptop's USB connector because it cannot communicate with the compliant USB device. Instead, the USB device can be charged by a dedicated USB charger (“dedicated charger”) which is essentially a power adapter with an AC input and a USB connector output. The dedicated charger has an identification protocol which lets a USB device know that it is connected to dedicated charger.
For example, an iPhone® smart phone from Apple, Inc. can be coupled to some PC-based laptop computers for charging through a USB connector port while the computer is operating in an S0 state. Typically, the iPhone will charge at a maximum rate of about 500 mA to prevent too much current being drawn from the laptop computer while it is operating. However, with many such laptop computers, if the computer goes into a standby (S3) or hibernate (S4) mode the iPhone will stop charging. With such systems, the iPhone can be disconnected from the computer and a mouse, keyboard, or other “remote wake-up” device can be connected to the USB connector port in order to “wake-up” the computer.
As used herein, a “USB remote wake-up device” is a device, such as mouse or keyboard, which can be coupled to a USB connector port and which can send a “wake-up” signal or command to the system (e.g. the laptop computer). The form of the command or signal can vary, e.g. in the case of a mouse it can be a “click” of a button, and in the case of a keyboard it can be the pressing of a key. It should be noted that, while USB remote wake-up devices can be of various types, they typically only draw enough power for their own operation and they tend to be low speed devices.
Some laptop computers have the ability to charge USB devices even when they are in a “sleep” state (e.g. S3 and/or S4 states). In fact, the rate of charging can increase during these modes because the computer system does not require the power. For example, a laptop computer provided with a MAX14550 USB host charger device allows a USB device to charge at about 500 mA during the computer's S0 state and at about 900 mA during the computer's S3 state.
While having certain advantages, prior systems which allow USB devices to charge in a standby mode tend to disable remote wake-up, i.e. the ability to unplug the USB device, plug in a “wake-up” peripheral such as a keyboard or mouse, and to wake-up the computer so that it is again in an S0 state.
These and other limitations of the prior art will become apparent to those of skill in the art upon a reading of the following descriptions and a study of the several figures of the drawing.